SAN FRANCISCO — Netflix’s video subscription service lost 800,000 customers in the third quarter — the biggest exodus in its history — even as its earnings rose 65 percent.

The losses were larger than management had previously warned. The unwelcome surprise, contained in financial results released Monday after the stock market closed, was compounded by its own forecast saying millions of Netflix Inc.’s DVD-by-mail subscribers could cancel the service in reaction to dramatic price increases that took effect last month.

The bad news bruised already battered stock as the shares plunged by more than 27 percent in after-hours trading after closing at $118.84 in regular trading.

Netflix lost its luster among consumers and investors by raising prices as much as 60 percent in the U.S. and bungling an attempt to spin off its DVD-by-mail rental service.

The company, based in Los Gatos, Calif., ended September with 23.8 million U.S. subscribers, down about 800,000, or 3 percent, from June. Netflix had predicted it would lose about 600,000 U.S. subscribers in a forecast released last month.

Management expects to gain U.S. subscribers in the current quarter. But a substantial number of Netflix’s customers are expected to choose between renting DVDs through the mail or streaming video over high-speed Internet connections instead of paying for both services.

The biggest hit is expected on the DVD side, which Netflix has been de-emphasizing to save money on mailing costs.

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